This invention relates to an ion-conductive polymer electrolyte.
As an ion-conductive polymer electrolyte, there has been known following compounds. For example, an organic polymer electrolyte of polyethylene oxide type; an organic polymer electrolyte having a multifunctional polyether molecular structure prepared by a random copolymerization of ethylene oxide portion and propylene oxide portion (Japanese Patent Publication No. 249,361 of 1987); an ion-conductive polymer electrolyte comprising a branched polyethylene oxide prepared by adding ethylene oxide as the side chain to a main chain of polyethylene oxide (Japanese Patent Publication No. 136,408 of 1988); a solid polymer electrolyte comprising an ethylene oxide copolymer containing an ionic compound in dissolved state (Japanese Laid-Open Patent Publication No. 83,249 of 1986); and an ion-conductive polymer electrolyte in which a high polymer solid substance having plasticity is further constituted substantially with a branched-chain of a homopolymer or copolymer which is thermoplastic and has no cross linkage (Japanese Laid-Open Patent Publication No. 98,480 of 1980).
However, those conventional ion-conductive polymer electrolytes have the following problems.
First, the organic polymer electrolyte of polyethylene oxide type shows a relatively good lithium-ion conductivity in the temperature range not lower than 40.degree. C., but the characteristic is lowered rapidly at the room temperature range of about 25.degree. C. Accordingly, it is very difficult to use the electrolyte for various applications such as battery, electrochromic and the like.
The organic polymer electrolytes described in Japanese Patent Publication No. 249,361 of 1987 and Japanese Patent Publication No. 136,408 of 1988 do not show rapid lowering of the lithium-ion conductivity at the room temperature range of about 25.degree. C., but the lowering proceeds at a temperature of not higher than 0.degree. C. which is considered as a practical temperature range. Therefore, a practical ion-conductivity can not be obtained.
The organic polymer electrolyte described in Japanese Laid-Open Patent Publication No. 83,249 of 1986 is an organic polymer prepared by a randam-copolymerization of ethylene oxide with the other monomer. The structure of the organic polymer resultantly becomes amorphous as a result by the random-copolymerization, but the amorphous structure is not sufficient by the difference of reactivity between each monomers so that the product quality tends to be unstable.
Further, since the organic polymer electrolyte described in Japanese Laid-Open Patent Publication No. 98,480 of 1980 is thermoplastic, a film formed with it is limited only to be simple and a good adhesion between the film and the electrode can not be obtained.
The object of the present invention is to solve such problems as described above and to provide an ion-conductive polymer electrolyte which shows an excellent ion conductivity and can be easily handled.